SUMMARY While the mechanisms modulating the transmission and perception of chronic pain differ between men and women, the exact neuroanatomical and molecular differences existing between the sexes remain only partly understood. This proposal focuses on the study of intracellular mechanisms that modulate symptoms of long-term pain states in female mice. We have identified signal transduction mechanisms in the mouse ventrolateral periaqueductal gray (vlPAG) that selectively modulate sensory components of inflammatory and neuropathic pain in female mice. The signal transduction modulator Regulator of G Protein Signaling-1 (RGSz1) controls the function of G protein coupled receptors (GPCRs) by binding to activated G?i subunits, including the Golgi enriched G?z. RGSz1 negatively modulates the amplitude and direction of signal transduction of several GPCRs involved in pain transmission and central sensitization, including the serotonin 5HT1A receptor and the membrane estrogen receptor GPER1. Our recent findings show that RGSz1 mRNA and protein levels are dynamically regulated in the vlPAG of female (but not male) mice by long-term peripheral inflammation. Constitutive deletion of the RGSz1 gene or vlPAG-specific knockdown of RGSz1, exacerbate sensory hypersensitivity behaviors such as thermal hyperalgesia and mechanical allodynia in female mice, but have no effect in male mice. We will apply several genetic mouse models for regional inactivation or overexpression of RGSz1 in vlPAG neuronal subsets, along with brain biochemistry and voltammetry to understand the sex-specific mechanism by which RGSz1 modulates the function of the descending inhibitory pathway and sensory hypersensitivity in models of peripheral inflammation and nerve injury. We will investigate the mechanisms regulating the expression of RGSz1 in the vlPAG and we will determine the role of RGSz1 in signal transduction and gene expression events underlying chronic pain states. We also will apply chronic pain models to understand the impact of RGSz1 on the expression of Golgi components and in the export of estrogen GPER1 receptors to the cell surface.